Device for control of current impulses



Nov; 28, 194.4.

J. B. WELCH DEVICE FOR CONTROL OF CURRENT IMPULSES Filed March 1, 1943 Patented Nov. .28, 1944 DEVICE FOR CONTROL OF CURRENT IMPULSES JeromeB. Weich, Milwaukee, Wis., assignor to \Cntler-Hammer, Inc., Milwaukee, Wla, a corporation of Delaware Application March 1, 1943, Serial-No. 77,567 '1 Claim. (01. 219-4) This invention relates to a device for control of current impulses. The invention relates more particularly to a brazing controller, and is especially adapted to the control of the current impulses supplied to a machine for joining parts by brazing or soldering.

To braze two parts together they are placed betweentwo relatively movable laws of a press so that the contacting surfaces which are to. be united are in line with the jaws and pressure is applied to the jaws and through them to the contacting surfaces. A quantity of 'a special brazing metal and flux may be interposed between the surfaces which are to be joined. I

The laws or electrodes are connected into a current supply circuit. Thereupon current is supplied to the circuit. The current in passing through the contacting surfaces heats the surrounding metal to melting temperature and the spots weld together while pressure thereon is continued.

if the current is supplied for too long a time, too much metal is melted and flows away from the spots or the metal is burned, resulting in a defective joint or weld. It is therefore important that the total amount of energy during a brazing cycle be accurately measured and controlled. It is further desirable that the initial current flow be at a relatively high rate, so as to rapidly heat the brazing metal to its melting temperature, and that thereafter the current be decreased to a relatively low value which nevertheless keeps the brazing metal and the pieces to be joined at a predetermined heat until the process is completed. I

An object of the present invention is to provide automatic means to aflord an initial high brazing current which is thereafter-reduced to a desired for regulating the time or duration of flow of brazing current. Another object is to provide adjustable means for automatically controlling the minimum and maximum current values during a brazing cycle.

nals of an alternating current supply of brazing energy. The drawing shows a piece of sheet metal I to which a relatively small silver button Another object is to provide novel means for ferred embodiment of the invention.

In the drawing, L and L designate the termior contact 2 is to be brazed. The two pieces are brought into register and are clampedbetween the laws 3 and 4 of a press, which may be operated manually as shown or in any other desired manner. One of the jaws 4 is stationary and is mounted upon the anvil of the press, while the law 3 is movable and as shown may be moved toward the jaw 4 by means of a lever B, which lever is provided with a, counterweight 5 or other biasing means to normally bias the jaw 3 to its retracted position. The welding energy is supplied to the laws 3 and 4 through a transformer 6 provided with a primary winding 1, equipped with a number of taps 1, 1'', l to which the circuit may be connected selectively in a known manner to provide for varying ratios of transformation of the transformer. The transformer 6 is provided with a secondary winding 8, the terminals of which are connected to the jaws 3 and 4, respectively, so that when two pieces whichare to be brazed are clamped between the jaws, the secondary circuit is closed and current passes therethrough in a well known manner upon completion of the circuit of primary winding 1.

To control continuit of the current supply from the lines L and L, the fixed terminal of the primary winding I is adapted to be connected to line L through normally open main contacts 9 of an electromagnetic control switch 9, which is also provided with an energizing winding 9 and with normally open auxiliary contacts 9. Connected in series with a selected tap (such as "l illustrated) of the primary winding 1 is the energizing winding ll of a variable reactance regulator ill. The winding ll may also be Drovided with a number of ta'ps ll", ll which permit variation of the number of active turns of said winding.

The winding l l is mounted upon a stationary substantially U-shapedmagnetic frame l2. Pivotally connected to said frame i2 is an armature i3, so shaped that in the extreme position illustrated a substantial air gap is provided in the term-magnetic circuit formed by said frame and armature, whereas in the other extreme position of armature I! said ferro-magnetic circuit is substantially closed.

The armature I 3 is normally biased to the lilustrated position of maximum air gap by means of a counterweight l4 mounted on a rearward extension l3 of said armature, while the clockwise movement of the armature is toward its other extreme position, under the influence of th pull exerted thereon by the magnetic flux induced by the coil II, is opposed by a timing device such as a dash-pot IS, the plunger of which is connected to a forward extension Ii! of the armature I3. The dash-pot I is provided with an adjustable valve I5 which permits adjustment of the rate of descent of the piston, so that the rat of clockwise movement of armature I3 for controlling time of closure of the magnetic air gap may. be regulated. The upward or counterclockwise movement of the armature I3 is not subjected to any substantial retarding action by the dash-pot I5. Any other suitable timing device which is adapted to regulate the movement of the armature in the manner described may be substituted for the dash-pot I5.

The maximum air gap position to which the armature I3 is biased by weight I4 may be preselected or'controlled by an adjusting screw I6, which abuts said rearward extension I3 of said armature, while the minimum air gap may similarly be preselected or controlled by an adjusting screw II.

The system also preferably includes a normally open foot-operated switch I8, which is adapted when closed to connect one terminal of the energizing winding 9 of switch 9 to line L through a normally closed switch I9; the other terminal of winding 9 being connected directly to line L The auxiliary normally open contacts 9 of switch 9 when closed provide a maintaining circuit for winding 9 independent of switch I8. An adjustable abutment 20 upon a further rearward extension III of armature I3 is adapted to effect opening of switch I9 when the armature I3 is moved clockwise to its attracted position.

The operation of the device is as follows: If it is desired to joint two pieces, connection is made to a suitable tap I I or 1 on the primary winding I and to a suitable tap II or II on the energizing winding II. The maximum air gap of the variable reactance regulator I0 is adapted to be adjusted by means of the screw IS; the minimum air gap is adjusted or preselected by the screw I1. and the relative time at which switch I9 is opened is preselected by adjustment of the abutor flux, if desired, and after applying the desired or required degree of pressure to the jaw 33, he

momentarily depresses the foot switch I8. This completes an energizing circuit from line L through winding 9, and switches I8 and I9 to line L This causes closure of the main contacts 9 of switch 9, whereupon the maximum current for which the system has previously been adjusted flows through the primary winding 1, and induces a current in the secondary winding 8 of the transformer 5. At the same time auxiliary contact 9 provide a maintaining circuit for winding 9 and the operator may therefore release the foot switch I8. The metal at the op posing surfaces which are to be joined is quickly melted and fills the space between said surfaces.

As soon as the primary transformer current flows, the magnetic flux induced in the frame I2 by the energizing coil II attracts the armature I3 and causes it to move downwardly thereby decreasing, the air gap which increases the impedance of the regulator III. The regulator I0, being in series with the primary winding I of the transformer 6, decreases the current flowing through the latter and thus decreases the secondary current of the transformer until the armature I3 has descended to its lowermost preselected or adjusted position, in which position of said armature the brazing current will have been reduced to the desired minimum, whereupon the switch I9 is opened. This deenergizes the magnet switch 9 and current is cut off from the transformer 6. The minimum current is preferably chosen so that, even with the welding current still flowing, the Jaws 3 and 4 may be separated while the secondary winding is still energized without causing any are to be formed between the movable jaw 3 and the completed article from which it is separated. This is particularly desirable if the switch I9 is omitted. It should also be pointed out that the jaws 3 and l are preferably not separated from each other until the metal which ha been melted by the maximum current has again solidified through sufficient reduction of the current, so that the parts being brazed adhere strongly to each other.

While the system has been explained in connection with a brazing or soldering process it will be obvious that it may also be used for electric spot-welding. In the latter case it is often desirable at first to supply a relatively small current to the surfaces to be welded and to increase this current when the metal at the weld softens and thus the contact surfaces between the parts to be welded is increased, which requires a higher current to maintain the material at the weld at weld ing temperature. Such regulation can be obtained by suitable modifications of the regulator shown, as will be apparent to those killed in the ar The invention has been explained in connection with a variable reactance regulator I0 having a correspondingly variable inductance. It is obvious that a regulator havinga variable capacitance arranged to vary the current supply through a condenser may be substituted therefor. In the system shown in the drawing current is supplied from a, constant voltage source of alternating current. It is also obvious that the current to the machine may be supplied from a constant current source of alternating current and that a part of the constant current may be shunted around the machine or the transformer supplying the same by a shunt connected variable reactance such as the variable inductor shown in the drawing or by a variable condenser. Further modifications of the device herein specifically illustrated will be obvious to those skilled in the art in the light of the foregoing description.

I claim:

In a current impulse controlling device, a transformer havin a primary winding and a secondary winding, electrodes connected with the respective terminals of said secondary winding and adapted for completion of the circuit of the latter upon pressure engagement of said electrodes with work interposed therebetween, a variable reactance regulator including an energizing winding connected in series with said primary winding, said regulator having a magnetic circuit associated with said energizing winding. means for initially providin a predetermined maximum air secondary windings to a corresponding minimum 10 value, adjustable means associated with said last mentioned means to control the eflect of said en ergizing winding upon the rate of reduction of said air gap from its maximum to its minimum value, said regulator acting automatically after a predetermined period of time to effect interruption of the circuit of said primary winding, and associated means adjustable at will to vary the length of said time period. I

JEROME B. WELCH. 

